The present invention relates to formulations of additives which, added for example to engine fuels, substantially reduce the tendency of the latter to form deposits and to corrode various parts of the engine.
The use of conventional fuels very often leads to the fouling of the various engine parts, due to the incomplete vaporization and combustion of the fuel in the inlet system and/or in the combustion chamber and to the presence of lubricant traces.
In the inlet system, the accumulation of these deposits can thus occur at the level of the injectors, the carburetor and the inlet valves.
Such an accumulation has harmful consequences on the level of the driving pleasure, with the appearance of an unsteady idling and misfires in spark ignition engines, as well as on the level of the optimum running of the engine through the modification of the fuel-air ratio owing to the adsorption-desorption phenomena of the fuel on the formed deposits.
In order to remedy this fouling, it is possible to carry out a periodic cleaning of the affected parts, especially the valves, which is particularly costly.
The accumulation of deposits in engines and particularly on inlet valves can also be reduced by using fuels which contain certain additives, for example detergent-type additives that are possibly combined with, for example, anticorrosive or antideposition additives for combustion chambers.
Additives, which are well-known in the trade, for example those of the polyisobutene-amine type, are usually associated with a mineral or a synthetic oil and may lead to an increasing fouling of the combustion chambers and thus to an increase in the octane requirement of the engine, with a higher sensitivity to knocks.
Among the numerous additives described in the prior art, the products of the condensation of polyalkenylsuccinic anhydrides on polyamines, such as for example tetraethylenepentamine, which are particularly described in U.S. Pat. No. 3,172,892, can be cited. These additives show good results as far as anticorrosive properties are concerned, but they are not efficient as valve detergents.
One can also cite the products of the condensation of polyalkenylsuccinic anhydrides on hydroxyimidazolines, and particularly on 1-(2-hydroxyethyl) imidazolines substituted in position 2 by an alkyl or an alkenyl group, such as those which are described in patent application EP-A-74,724. The products described in this application are good additives for engine fuels and their anticorrosive action is considerable, but they are not very efficient at the level of the carburetor detergency.
Most commercial additives are mostly used in association with a mineral oil the main function of which is to increase or obtain the necessary "valve" detergency.
The use of a mineral oil usually causes a relatively considerable fouling of the combustion chamber, which is harmful to the good running of the engine. The viscosity of the additive concentrate obtained by adding the mineral oil is usually relatively high, which may cause difficulties as far as material handling and additivation (addition of additive to the fuel) are concerned. Besides, the additive concentrates comprising a mineral oil show a bad cold-resistance.